http://uwb25d43nnzerbozmtviwn7unn7ku226tpsjyhy5n4st5cf3d4mtflqd.onion/posts/metadata/index.html
You can verify that the metadata has been removed by re-adding the cleaned file and viewing its metadata. When you clean a PDF file, it is converted to images, so the quality is downgraded and you cannot select the text in it. If you want to retain this ability, there is a lightweight cleaning mode that cleans only the superficial metadata of your file, but not the metadata of "embedded resources" (such as images in the PDF).